LIFE SCIENCES

Grade 12

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DNA – THE CODE OF LIFE 05 JULY 2014

Lesson Description

In this lesson we

Answer questions on: o DNA, RNA and Protein synthesis o The processes of mitosis and meiosis o Comparison of the processes of meiosis and mitosis o The importance of meiosis o Abnormal meiosis occurs and its consequences

Summary

Test Yourself

Select the most correct answer from the options given. Write down only the correct letter

Question 1

Which of the following statements are characteristic of DNA?

(i) Double-stranded helix

(ii) Sugar molecule is ribose

(iii) Found in the nucleus

(iv) Constant amount normally found in all the somatic cells of a particular species

A. (i), (ii) and (iii) only

B. (i), (ii) and (iv) only

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C. (i), (iii) and (iv) only

D. (i), (ii), (iii) and (iv)

Question 2

The following data represents a small section of a sequence of nucleic acid bases taken from an animal cell:

A G C U C G U U

From this data it is reasonable to conclude that …

A. this portion of nucleic acid will code for a chain of eight amino acids.

B. the sequence given will be complementary to the sequence C T C G T G C T T.

C. the nucleic acid shown contains the sugar ribose.

D. the nucleic acid shown is DNA.

Question 3

The list below provides information relating to the replication of DNA:

1. Complementary nucleotides bind to each of the two strands. 2. Sugar phosphate bonds form between the nucleotides. 3. The newly formed DNA molecules are identical to each other. 4. After unwinding, the DNA molecule forms two single strands.

The correct order of these events as they occur in DNA replication is …

A 1, 2, 3 and 4.

B 1, 2, 3 and 2.

C 4, 2, 1 and 3.

D 4, 1, 2 and 3.

Question 4

In an investigation it was found that 10% of the bases in a molecule of DNA were thymine. What was the ratio of thymine to guanine in the same molecule?

A 1:2

B 1:3

C 1:1

D 1:4

Question 5

A ring of bacterial DNA that is found in addition to the organism's main DNA is known as a …

A protein

B plasmid

C genome

D triplet

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Question 6

The relationship between nucleic acids and nucleotides is that ...

A nucleotides are building blocks of nucleic acids.

B nucleic acids are building blocks of nucleotides.

C nucleotides are larger than nucleic acids.

D nucleic acids are found in the nucleus and nucleotides are found in the cytoplasm.

Question 7

The structure of RNA ..

A guanine pairs with thymine.

B guanine pairs with adenine.

C adenine pairs with thymine

D adenine pairs with uracil.

Question 8

If one side of a DNA molecule contains the following sequence of nucleotides, AGTCCG, the complementary sequence on the codon would be:

A TCAGGC

B AGTCCG

C UCAGGC

D UCUGGC

Question 9

The repeating units in both DNA and RNA are called:

A nucleotides

B amino acids

C nucleic acids

D hydrogen bonds

Question 10

Which of the following undergo meiosis?

A sperm cells

B haploid cells in the ovary

C liver cells

D diploid cells in the testes

Question 11

Give the correct biological term for each of the following descriptions. Write only the term next to the question number

1. The two parts of a chromosome held together by a centromere 2. A pair of chromosomes, one inherited from each parent, that have the same genes at the

same loci 3. The point at which chromatids of homologous chromosomes cross over during meiosis

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4. The process by which the DNA molecule makes a copy of itself 5. The phase in meiosis where the DNA molecule makes a copy of itself 6. The phase in meiosis which results in the halving of the chromosome number 7. An arrangement of black bars representing DNA fragments that can be used to determine

whether people are related

Question 12

Indicate whether each of the statements in COLUMN I applies to A only, B only, both A and B or none of the items in COLUMN II. Write A only,B only, both A and B or none

COLUMN I COLUMN II

1 Chromosome condition of a cell that

has a single set of chromosomes

A: Haploid

B: Diploid

2 Causes of variation during

meiosis

A: Random fertilisation

B: Random mating

3 Increases variation in a species

A: Cloning

B: Mutation

4 Discovered the double helical structure

of DNA

A: Francis Crick

B: James Watson

Question 13

The diagrams below show cells dividing during meiosis

1 2 3

4

5

D

A

B

C

E

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13.1 Give the names of the parts labelled A to E respectively. (5)

13.2 Identify the phase represented in:

a.) Diagram 1 (1)

b.) Diagram 2 (1)

13.3 Write down the numbers of the diagrams in the correct sequence in which the phases occur. (3)

13.4 State TWO ways in which meiosis is important. (2)

Exam Questions

Question 1

(Adapted from March 2014, Paper 1)

A pair of chromosomes, one inherited from each parent, that have the same genes at the same loci

1.1 Identify the parts labelled A and B.

1.2. State whether the phase of meiosis shown above is a part of Meiosis I or Meiosis II.

1.3. Give ONE visible reason for your answer to QUESTION 1.1.

1.4. Answer the following questions:

(a) How many chromosomes are present in the cell above?

(b) How many chromosomes will be present in each cell at the end of meiosis?

1.5. Could the cell represented in the diagram be that of a human?

1.6. Explain your answer to QUESTION 1.5.

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Question 2

The diagram below shows the result of abnormal meiosis, starting with a cell showing chromosome pair 21.

2.1 Explain the number of chromosomes present in sperm R and sperm T.

2.2 How many copies of chromosome 21 would you expect in a normal gamete?

2.3 What genetic disorder will result if sperm U fertilises a normal ovum?

2.4 Describe TWO ways in which meiosis contributes to genetic variation.

Question 3

The diagram below shows the structure of part of a DNA molecule. Study the diagram and answer the questions

3.1 Name the structures labelled A, B, C and D. (4)

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3.2 What are the components of a nucleotide? (3)

3.4 Explain how this molecule makes a copy of itself. (4)

3.5 Tabulate THREE differences between DNA and ribonucleic acid (RNA). (7)

Question 4

The diagram below shows the process of protein synthesis.

4.1 Identify the following:

(a) Molecule X (b) Organelle Y

4.2 Identify the nitrogenous base labelled:

(a) 1 (b) 3

4.3 Describe the role of DNA during transcription.

4.4 Describe the part of protein synthesis shown as process W, which occurs at organelle Y.

4.5 The table below shows the amino acids that correspond with different DNA codes.

Write down the correct sequence of amino acids coded for by structure S in the diagram.

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Question 5

(Adapted from March 2014, Paper 1)

Start with a cell containing FOUR chromosomes and describe ALL the chromosomal changes that occur during meiosis, resulting in the formation of abnormal gametes due to non-disjunction in meiosis 1.

Content: (17)

Synthesis: (3)

(20)